Translation
The one who has THE SON [OF GOD] has life; the one who does not have THE SON OF GOD does not have life.
Paraphrase
Anyone who has received the rule of GOD over his life has also received the reward of true life and thus knows what living really means; the one who has not received the rule of GOD over his life has not received the reward of true life and has no clue what living really means.